The development and function of the nervous system relies on its ability to form specific neuronal circuits and to alter their properties in response to neuronal activity and signaling. Spatially restricted modification represents one of the key problems in the regulation of neuronal plasticity. That is, mechanisms need to exist that enable the modification and generation of proteins locally, e.g. changes that occur at only one synapse but not at others. The goal of this proposal is to explore whether alternative splicing of mRNAs occurs in the neuronal cytoplasm and can be locally controlled by synaptic signaling mechanisms. To address this question, we will focus on the alternative splicing of a family of neuronal cell surface receptors, called neurexins, which exist in more than 1,000 functionally different splice variants. Neurexin splicing will be analyzed using a combination of RT-PCR, fluorescent in situ hybridization, and splice-form specific antibodies. The aims of this proposal are (1) to characterize cytoplasmic intron-containing neurexin pre-mRNAs, (2) to analyze the splicing machinery that can remove introns from pre-mRNAs in the neuronal cytoplasm, and (3) to investigate the regulation of neurexin splicing in response to neuronal activity and signaling. Findings from this research will provide twofold contributions: First, they will provide novel insights into the mechanisms and regulation of neurexin protein expression and function. Secondly, the principal mechanisms that control cytoplasmic splicing in neuronal cells are likely not restricted to splicing of neurexin proteins but may also control expression of other neuronal proteins. The characterization of local splicing at synapses would support a novel mechanism for regulating neuronal plasticity and function. The findings from these studies have direct relevance for human health. Neurexin splicing is differentially regulated in ischemia. Moreover, splicing of neurexins regulates the interaction of neurexins with two ligands, neuroligins and alpha-dystroglycan. Both ligands have been implicated in nervous system disorders: neuroligins in mental retardation and autism and alpha-dystroglycan in muscular dystrophies. Information obtained in studies on neurexin splicing will therefore also be valuable for understanding aspects of cellular and molecular defects underlying these disorders. [unreadable] [unreadable]